Cracking the shellcode

In this section, we will take a look at the code that gets executed by the attacker during vulnerability exploitation. This code gets executed in very special conditions without headers and known memory addresses. Let’s learn what shellcode is and how it’s written for Linux (Intel and ARM processors) and, later, the Windows operating system.

What’s shellcode?

Shellcode is a list of carefully crafted instructions that can be executed once code has been injected into a running application. Due to most of the exploit’s circumstances, the shellcode must be position-independent code (which means it doesn’t need to run in a specific place in memory or require a base relocation table to fix its addresses). Shellcode also has to operate without an executable header or a system loader. For some exploits, it can’t include certain bytes (especially null for the overflows of the string-type buffers).

Now, let’s take...